By the amount of white and size of comb, I'll say roo. When I got my BCMs, the boys became obvious very early - 3 weeks or so. I read somehwere that the girls tend to have darker chests than the boys as chicks.
My Maran has almost no comb and she is 17 days, so I'm going to hop in the bandwagon and say rooster.
The colour shows a bit of hope though if you want a hen, typically Marans will be darker if they're female chicks and lighter as a male. They could always lighten up of course though.
I too have my suspicions that this little one will indeed be a roo, will keep you all posted with pics, did initially want a hen to complete my trio but it now means I can hatch more eggs! won't be until next year now though so I'll just have to be patient
does anyone know if a bcm roo crossed with either a Rhode island red or light sussex will produce hens which are dark egg layers? as this is why I like marans